Your rectifier might be good, I can't tell for certain with the data you've given.
Some notes on resistance. Low resistance means values approaching zero ohms. High resistances are larger numbers with infinity being the upper limit.
What meter are you using for resistance checks? Modern meters usually have a diode symbol range setting. This setting puts extra power into the circuit under test so that diodes have enough to conduct when forward biased. Other ranges won't have enough power to turn the diode on and it may read open with both polarities. This is not an issue with the old coal fired ohmmeters.
Their measuring circuits aren't very sensitive, so they put plenty of power into the circuits they test.
Field coil looks good.
Don't worry about the regulator yet. Yes, in theory the black and white should test the same. There are contacts inside that spark when interrupting current flow. This action can actually improve contact resistance as well as degrade it. We'll revisit those contacts after we start getting 14.5 V regulation and the vreg is doing some contact chattering rather than simply passing system voltage to the field coil.
Quick lesson.
The amount of voltage lost through a high resistance connection is directly proportional to the current passing though it. It is a function of ohms law. E (voltage) = I (current) X R ( resistance)
Example: lets use a constant 12V source, a known 0.1 ohm connection resistance and a load device that consumes either 10 amps or 1 amp.
When 1 amp is selected, the voltage loss through the connection is 0.1 volt. The load device sees 11.9 V of the source 12 V.
When 10 amps is selected, the voltage loss through the connection is 1.0 volt. The load device sees 11.0 V of the source 12 V.
Now imagine that there are ten connections between the power source and the load device.
When the 1 amp load is selected, the total voltage loss through ten connections is 1.0 volts. The load device sees 11.0 V of the source 12 V.
When 10 amps is selected, the voltage loss through ten connections is 10.0 volts. The load device sees 2.0 V of the source 12 V.
In reality your headlight, or for that matter, most all of the power consumers on your bike are not constant current loads, but draw commensurate with the voltage they receive. Your 60 Watt headlight, for example will draw 5 amps when fed 12 Volts. It will draw 4.2 Amps when fed 10 V and produce light like a 42 watt headlight.
Your immediate concern is that the black wire off the ignition switch is somewhere in the middle of your 10 or more series of connections shared with other devices. As long as your connectors and switches provide non-zero in-line resistance, the total operating load placed on the black wires is going to change the voltage readings you take.
In other words, when you make voltage readings to compare to previous tests, make sure the load conditions are the same. And, just to make it more interesting, note that the voltage of the battery drops as it depletes. So, to know the voltage drop at load, you need to always compare to the "right now" voltage at the battery.
The reason why I explained this is that the new voltage readings in your recent message can only be compared to ones from your previous post, if the test conditions were identical. Can you verify they were?
I don't want to discourage you from connector cleaning. I'm just looking for quantifiable data to show you are doing the most important ones first.
The data presented so far seems to suggest you've got more cleaning to do. Look at your schematic. Follow power path from battery to alternator field and to the rectifier. Note each connector or switch in the path. Each one has the potential for voltage loss. Don't forget the ground path, too, as it is in the current loop and can consume power, as well.
Cleaning connectors-
Male terminals you already know how to access and clean with a Scotchbrite pad. The female bullets are more interesting. I made a tool to clean these. I got a piece of brass tubing from the hardware store in a smaller diameter than the bullet males. I also bought some crocus or emery cloth. Very fine abrasive, I think it has a coating of red jewelers polishing rouge on one side. I used a razor saw to cut a slot in the end of the tubing wide enough to accept the thickness of the cloth. Cut widths of cloth about the length of the bullet male and make the strips long enough to wrap around the end of the tube with the abrasive exposed. Chuck the tube in your electric drill and insert into the female connector. As the drill spins it cleans and polishes the contact surface. You can adjust the number of wraps to make good pressure inside. If needed, readjust the female socket tension for a good grab onto the cleaned male bullet. Just before final assembly, I squirt a little DeOxit on both the male and female connectors.
The new tool makes the female bullet contacts easier and faster to clean than the males!
Female spade terminals I clean with a modified thin fingernail file about the same or less thickness than the male spade terminal. It was well used and not very aggressive cutting. I ground one so its width was about the same as the male spade. I made mine cut on extraction from the female spade socket. One or two insertion/extraction cycles is usually all it takes to clean the terminal. The male terminals are exposed to cleaning like the Bullet type. A little DeOxit and reassemble.
Cheers,
